The present invention relates in general to off-shore stations and in particular to a new and useful foot joint for connecting a movable service tower of an off-shore station to a fixed foundation at the sea bottom.
A foot joint for a movable service tower of an off-shore station is known from German patent No. 2,549,859. In this construction, the joint part secured to the foot of the tower is designed as an external spherical zone moving with the tower while sliding on a stationary spherical joint part which is immovably connected to the foundation. The design of the sliding surfaces of such a ball joint is described in German OS No. 27 55 592. In the sliding zone between the two hemispherical shells, exchangeable spherical sliding shoes are secured to one part, and slide on the spherical surface of the opposite part while the spherical gap therebetween is maintained and are lined with a material having a low coefficient of friction. The sliding zone between the hemispherical shells is protected from above and below by annular seals closing the gap therebetween.
The sliding shoes in the relatively narrow gap between the hemispherical shells are accessible only upon removing the upper seal. Consequently, no visual monitoring of the function and condition is possible. Because of the narrow space and the geometry of the gap, the exchange of the spherical sliding shoes and of the upper seal is difficult. The manufacture of the ball joint, especially the working of the hemispherical shells and the sliding shoes, is very expensive.